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The present work reports a systematic study on the structural, thermal, electrical and electrochemical stability of SrCo1−xNbxO2.5+δ series as a potential reversible oxygen-electrode for intermediate-temperature solid oxide fuel cells. The identified best composition is x = 0.10, which exhibits a stable pseudo primitive cubic structure at <700°C and a reversible oxygen redox reaction at 350°C. The conductivity of this material is p-type and also exhibits a peak at 350°C, implying that the electron hole conduction is closely associated with the oxygen nonstoichiometry. Electrochemical impedance spectroscopy analysis indicates a low polarization resistance rate-limited by a slower surface O2 dissociation step. Overall, the material is thermally stable and oxygen redox reversible below 700°C, above which a catalytically less active brownmillerite SrCoO2.5 is formed.